In last week’s blog, we took a look at some risk factors that can place excessive valgus, or inside out, force on the elbow and place pitchers at higher risk for developing injury to their medial ulnar collateral ligament (MUCL), which is repaired by the famous Tommy John surgery. These risk factors included a larger carrying angle of the elbow, higher throwing velocities, and higher pitch counts. This week we are looking at the most complex risk factor that can place additional valgus stress on the elbow and subsequently the MUCL: pitching mechanics. Not to be overlooked, pitching mechanics are extremely important to analyze in both young and elite players because it is a modifiable risk factor! We can do something about this through training.

Let’s start off by talking about the phases of throwing and proper throwing mechanics before we delve into what throwing deviations put excess stress on the elbow. Glenn Fleisig at the American Sports Medicine Institute in Birmingham Alabama has written a great paper on the six phases of throwing (wind up, stride, arm cocking, arm acceleration, arm deceleration, follow through) and normal mechanics.

The wind up is the motion from when the pitcher starts moving until he has reached a balanced position with the lead knee at maximum height of its kick. This phase can be slow when pitching from a full wind up or quicker if pitching from the stretch when runners are on base. However, in either case the arm moves very little and injuries are rare during this phase of throwing.

The stride phase includes the point from a balanced position until the lead foot hits the ground. Stride length should be 83% of body height, lead knee flexion should be 45 degrees, pelvis rotated 33 degrees towards batter, and shoulders only about 15 degrees open. The arms separate down and up so that the throwing shoulder should be abducted 93 degrees, elbow flexed 90 degrees, and shoulder externally rotated 56 degrees.

The arm cocking phase is from lead foot contact until the arm reaches maximal shoulder external rotation (MER), which can reach as much as 181 degrees. The amount of external rotation is related to ball velocity, but also a point of injury. Trunk rotation is an important aspect of the cocking phase as the glove hand is pulled into the body to help accelerate rotational velocities of the hips and upper trunk, which have a slight lag between them.

During arm deceleration, the rotator cuff must work eccentrically to resist shoulder distraction as the ball is released and the shoulder maximally internally rotates. The follow through phase starts at peak shoulder internal rotation and goes until the end of the pitching motion.

Now that we know what normal pitching mechanics look like, let’s take a look at what deviations can occur that cause increased elbow valgus stress and risk for medial ulnar collateral ligament injury. A popular article by Werner et al looked at pitching mechanics and medial elbow stress found that four aspects of overhead throwing were responsible for 97% of the variance in elbow valgus stress during a regression analysis. These included:

Shoulder abduction angle at foot contact

Elbow angle at peak valgus stress

Peak shoulder external rotation torque

Peak shoulder horizontal adduction angular velocity

The shoulder abduction angle is the angle of horizontal abduction that occurs between the humerus and the plane of the scapulae, which becomes larger the more the elbow trails behind the shoulder during a throw. This is also known as hyperangulation and the larger this angle the more valgus stress is placed on the medial elbow. Hyperangulation occurs during the arm cocking phase and can carry into the acceleration phase of throwing.

The amount of elbow flexion at peak valgus stress during a throw also determines how much stress is placed on the medial elbow. A more flexed elbow will help reduce the valgus forces on the elbow, while a straighter arm will increase this force. Average elbow flexion during the acceleration phase is 98 degrees.

Peak shoulder external rotation torque is the force that rotates the arm backwards during the cocking phase and beginning of the acceleration phase. This force averages 111 Nm for professional pitchers, and is impossible to measure through observation of the pitching motion and requires state of the art equipment that can measure angles and velocities in real time during a throw. Peak shoulder horizontal adduction angular velocity also requires measurement in a clinic and is a measure of how quickly the humerus, or upper arm, is moved forward toward the batter during the acceleration phase. The velocity averages about 933 degrees/sec in elite level pitchers.

As you can see the pitching motion is an explosive movement and quite complex due to the many joints involved. Valgus torque on the elbow can be limited with modifications in biomechanics, but it is difficult to see and measure in real-time. This is why at Competitive Edge Physical Therapy we use 3-dimensional body mapping using IMU (inertial measurement unit) sensors and slow-motion video analysis to help break down all the complex movements of the body. Our goal is to help athletes and active individuals improve their performance and reach their goals by using movement data! If you are interested in learning more about throwing mechanics and preventing injuries, come check out our state-of-the-art clinic here in San Jose or go to our website for more information!